One is a sending line to the lspv the other is the return line. I wouldn't recommend deleting it. If you ever haul anything in the bed it won't brake as well. Toyota engineering > forums in this case.

 

The LSPV adjusts the proportion of the rear to front braking pressures. The more weight over the rear axle, the lower the truck will sag over the axle. This will change the LSPV, to which there is a bar from the axle, and apply more or less pressure to the rear brakes relative to the front. The more weight in the back, the more rear braking relative to the front. If you read the FSM on testing the braking pressures, it will become pretty easy to figure it all out.
It's actually a good idea to take the small bar connecting the LSPV to the axle off, and move it through it's entire range before bleeding the LSPV. It can clog up over the years, and often this will break the clog up and allow you to get it out when you bleed the LSPV.

Does this help at all?
Pat☺

 

I took my lspv apart and cleaned. It was actually pretty simple. It had a surprising amount of sludge in it.

 

An update. The leak was caused by corrosion in the hard line. Both hard lines were in pretty bad shape from sitting in sludge,mud,wet pine needles......etc............The holes that would usually allow the water to drain were clogged up. Considering where this truck has gone in it's life I get it. If you do a lot of off road I suggest periodically clean the channel where the brake lines run. The lines for my truck (1993 SR5) are discontinued so the new ones will have to be manually shaped and fitted. The shop that's doing the work said the bill will be 3 to 350. I hope so. I can deal with that. Thanks to all that helped me get this together. I should be picking up the truck tomorrow. (Friday the 15th). I hope they don't find any other issues.

 

Thanks for the update!

I bet this will help another who encounters this problem. Good update indeed.

Have fun, now
Pat☺